Architecture and interconnect scheme for programmable logic circuits

ABSTRACT

An architecture of hierarchical interconnect scheme for field programmable gate arrays (FPGAs).

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/630,679filed Dec. 3, 2009, which is a continuation of U.S. Pat. No. 7,646,218filed Jun. 24, 2008, which is a continuation of U.S. Pat. No. 7,409,664filed Dec. 9, 2005, which is a continuation of U.S. Pat. No. 7,017,136,filed Oct. 23, 2003, which is a continuation of U.S. Pat. No. 6,703,861,filed Oct. 11, 2002, which is a continuation of U.S. Pat. No. 6,507,217,filed Sep. 13, 2001, which is a continuation of U.S. Pat. No. 6,433,580,filed Mar. 2, 1998, which is a continuation of application Ser. No.08/484,922, filed Jun. 7, 1995, which is a continuation of U.S. Pat. No.5,457,410 filed Aug. 3, 1993, which are all herein incorporated byreference.

TECHNICAL FIELD

The present invention pertains to the field of programmable logiccircuits. More particularly, the present invention relates to anarchitecture and interconnect scheme for programmable logic circuits.

BACKGROUND

When integrated circuits (ICs) were first introduced, they wereextremely expensive and were limited in their functionality. Rapidstrides in semiconductor technology have vastly reduced the cost whilesimultaneously increased the performance of IC chips. However, thedesign, layout, and fabrication process for a dedicated, custom built ICremains quite costly. This is especially true for those instances whereonly a small quantity of a custom designed IC is to be manufactured.Moreover, the turn-around time (i.e., the time from initial design to afinished product) can frequently be quite lengthy, especially forcomplex circuit designs. For electronic and computer products, it iscritical to be the first to market. Furthermore, for custom ICs, it israther difficult to effect changes to the initial design. It takes time,effort, and money to make any necessary changes.

In view of the shortcomings associated with custom IC's, fieldprogrammable gate arrays (FPGAs) offer an attractive solution in manyinstances. Basically, FPGAs are standard, high-density, off-the-shelfICs which can be programmed by the user to a desired configuration.Circuit designers first define the desired logic functions, and the FPGAis programmed to process the input signals accordingly. Thereby, FPGAimplementations can be designed, verified, and revised in a quick andefficient manner. Depending on the logic density requirements andproduction volumes, FPGAs are superior alternatives in terms of cost andtime-to-market.

A typical FPGA essentially consists of an outer ring of I/O blockssurrounding an interior matrix of configurable logic blocks. The I/Oblocks residing on the periphery of an FPGA are user programmable, suchthat each block can be programmed independently to be an input or anoutput and can also be tri-statable. Each logic block typically containsprogrammable combinatorial logic and storage registers. Thecombinatorial logic is used to perform boolean functions on its inputvariables. Often, the registers are loaded directly from a logic blockinput, or they can be loaded from the combinatorial logic.

Interconnect resources occupy the channels between the rows and columnsof the matrix of logic blocks and also between the logic blocks and theI/O blocks. These interconnect resources provide the flexibility tocontrol the interconnection between two designated points on the chip.Usually, a metal network of lines run horizontally and vertically in therows and columns between the logic blocks. Programmable switches connectthe inputs and outputs of the logic blocks and I/O blocks to these metallines. Crosspoint switches and interchanges at the intersections of rowsand columns are used to switch signals from one line to another. Often,long lines are used to run the entire length and/or breadth of the chip.

The functions of the I/O blocks, logic blocks, and their respectiveinterconnections are all programmable. Typically, these functions arecontrolled by a configuration program stored in an on-chip memory. Theconfiguration program is loaded automatically from an external memoryupon power-up, on command, or programmed by a microprocessor as part ofsystem initialization.

The concept of FPGA was summarized in the sixty's by Minnick whodescribed the concept of cell and cellular array as reconfigurabledevices in the following documents: Minnick, R. C. and Short, R. A.,“Cellular Linear-Input Logic, Final Report,” SRI Project 4122, ContractAF 19(628)-498, Stanford Research Institute, Menlo Park, Calif., AFCRL64-6 DDC No. AD 433802 (February 1964); Minnick, R. C., “Cobweb CellularArrays,” Proceedings AFIPS 1965 Fall Joint Computer Conference, Vol. 27,Part 1 pp. 327-341 (1965); Minnick, R. C. et al., “Cellular Logic, FinalReport,” SRI Project 5087, Contract AF 19(628)-4233, Stanford ResearchInstitute, Menlo Park, Calif., AFCRL 66-613, (April 1966); and Minnick,R. C., “A Survey of Microcellular Research,” Journal of the Associationfor Computing Machinery, Vol. 14, No. 2, pp. 203-241 (April 1967). Inaddition to memory based (e.g., RAM-based, fuse-based, orantifuse-based) means of enabling interconnects between devices, Minnickalso discussed both direct connections between neighboring cells and useof busing as another routing technique. The article by Spandorfer, L.M., “Synthesis of Logic Function on an Array of Integrated Circuits,”Stanford Research Institute, Menlo Park, Calif., Contract AF19(628)2907, AFCRL 64-6, DDC No. AD 433802 (November 1965), discussedthe use of complementary MOS bi-directional passgate as a means ofswitching between two interconnect lines that can be programmed throughmemory means and adjacent neighboring cell interconnections. InWahlstrom, S. E., “Programmable Logic Arrays—Cheaper by the Millions,”Electronics, Vol. 40, No. 25, 11, pp. 90-95 (December 1967), aRAM-based, reconfigurable logic array of a two-dimensional array ofidentical cells with both direct connections between adjacent cells anda network of data buses is described.

Shoup, R. G., “Programmable Cellular Logic Arrays,” Ph.D. dissertation,Carnegie-Mellon University, Pittsburgh, Pa. (March 1970), discussedprogrammable cellular logic arrays and reiterates many of the sameconcepts and terminology of Minnick and recapitulates the array ofWahlstrom. In Shoup's thesis, the concept of neighbor connectionsextends from the simple 2-input 1-output nearest-neighbor connections tothe 8-neighbor 2-way connections. Shoup further described use of bus aspart of the interconnection structure to improve the power andflexibility of an array. Buses can be used to route signals overdistances too long, or in inconvenient directions, for ordinary neighborconnections. This is particularly useful in passing inputs and outputsfrom outside the array to interior cells.

U.S. Pat. No. 4,020,469 discussed a programmable logic array that canprogram, test, and repair itself. U.S. Pat. No. 4,870,302 introduced acoarse grain architecture without use of neighbor directinterconnections where all the programmed connections are through theuse of three different sets of buses in a channeled architecture. Thecoarse grain cell (called a Configurable Logical block or CLB) containsboth RAM-based logic table look up combinational logic and flip flopsinside the CLB where a user defined logic must be mapped into thefunctions available inside the CLB. U.S. Pat. No. 4,935,734 introduced asimple logic function cell defined as a NAND, NOR or similar types ofsimple logic function inside each cell. The interconnection scheme isthrough direct neighbor and directional bus connections. U.S. Pat. Nos.4,700,187 and 4,918,440 defined a more complex logic function cell wherean Exclusive OR and AND functions and a register bit is available andselectable within the cell. The preferred connection scheme is throughdirect neighbor connections. Use of bi-direction buses as connectionswere also included.

Current FPGA technology has a few shortcomings. These problems areembodied by the low level of circuit utilization given the vast numberof transistors available on chip provided by the manufacturers. Circuitutilization is influenced by three factors. The first one at thetransistor or fine grain cell level is the function and flexibility ofthe basic logic element that can be readily used by the users. Thesecond one is the ease in which to form meaningful macro logic functionsusing the first logic elements with minimum waste of circuit area. Thelast factor is the interconnections of those macro logic functions toimplement chip level design efficiently. The fine grained cellarchitectures such as those described above, provided easily usable andflexible logical functions for designers at the base logic elementlevel.

However, for dense and complex macro functions and chip level routing,the interconnection resources required to connect a large number ofsignals from output of a cell to the input(s) of other cells can bequickly exhausted, and adding these resources can be very expensive interms of silicon area. As a consequence, in fine grained architecturedesign, most of the cells are either left unused due to inaccessibility,or the cells are used as interconnect wires instead of logic. This addsgreatly to routing delays in addition to low logic utilization, orexcessive amount of routing resources are added, greatly increasing thecircuit size. The coarse grain architecture coupled with extensiverouting buses allows significant improvements for signals connectingoutputs of a CLB to inputs of other CLBs. The utilization at the CLBinterconnect level is high. However, the difficulty is the partitioningand mapping of complex logic functions so as to exactly fit into theCLBs. If a part of logic inside the CLB is left unused, then theutilization (effective number of gates per unit area used) inside theCLB can be low.

Another problem with prior art FPGAs is due to the fact that typically afixed number of inputs and a fixed number of outputs are provided foreach logic block. If, by happenstance, all the outputs of a particularlogic block is used up, then the rest of that logic block becomesuseless.

Therefore, there is a need in prior art FPGAs for a new architecturethat will maximize the utilization of an FPGA while minimizing anyimpact on the die size. The new architecture should provide flexibilityin the lowest logic element level in terms of functionality andflexibility of use by users, high density per unit area functionality atthe macro level where users can readily form complex logic functionswith the base logic elements, and finally high percentage ofinterconnectability with a hierarchical, uniformly distributed routingnetwork for signals connecting macros and base logic elements at thechip level. Furthermore, the new architecture should provide users withthe flexibility of having the number of inputs and outputs forindividual logical block be selectable and programmable, and a scalablearchitecture to accommodate a range of FPGA sizes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a block diagram of a field programmable gate array logic uponwhich the present invention may be practiced.

FIG. 2A shows one example of an individual cell.

FIG. 2B shows another example of an individual cell.

FIG. 3A shows a logical cluster.

FIG. 3B shows the extension of I-matrix intraconnections of a logicalcluster to a neighboring logical cluster.

FIG. 4A shows an example of a logical cluster with vertical blockconnectors.

FIG. 4B shows an example of a logical cluster with horizontal blockconnectors.

FIG. 5A shows the eight block connector to level 1 MLA exchange networksassociated with a logical block and level 1 MLA turn points.

FIG. 5B shows a level 1 MLA turn point.

FIG. 5C shows an exchange network.

FIG. 6 shows the routing network for a block cluster.

FIG. 7A shows the block diagram of a block sector.

FIG. 7B shows a level 1 to level 2 MLA routing exchange network.

FIG. 8A shows a sector cluster.

FIG. 8B shows a level 2 to level 3 MLA routing exchange network.

DETAILED DESCRIPTION

An architecture and interconnect scheme for programmable logic circuitsis described. In the following description, for purposes of explanation,numerous specific details are set forth, such as combinational logic,cell configuration, numbers of cells, etc., in order to provide athorough understanding of the present invention. It will be obvious,however, to one skilled in the art that the present invention may bepracticed without these specific details. In other instances, well-knownstructures and devices are shown in block diagram form in order to avoidunnecessarily obscuring the present invention. It should also be notedthat the present invention pertains to a variety of processes includingbut not limited to static random access memory (SRAM), dynamic randomaccess memory (DRAM), fuse, anti-fuse, erasable programmable read onlymemory (EPROM), electrically erasable programmable read only memory(EEPROM), FLASH, and ferroelectric processes.

Referring to FIG. 1, a block diagram of a field programmable gate arraylogic upon which the present invention may be practiced is shown as 100.The I/O logical blocks 102, 103, 111 and 112 provide an interfacebetween external package pins of the FPGA and the internal user logiceither directly or through the I/O to Core interface 104, 105, 113, and114. Four interface blocks 104, 105, 113, and 114 provide decouplingbetween core 106 and the I/O logic 102, 103, 111, and 112. Core 106 iscomprised of a number of clusters 107 which are intraconnected byI-Matrix 101 and interconnected by MLA routing network 108.

Control/programming logic 109 is used to control all of the bits forprogramming the bit and word lines. For anti-fuse or fuse technology,high voltage/current is applied to either zap or connect a fuse. ForEEPROM, Flash, or ferroelectric technology, there is an erase cyclefollowed by a programming cycle for programming the logic states of thememory bits. In order to minimize skewing, a separate clock/reset logic110 is used to provide clock and reset lines on a group basis.

In the currently preferred embodiment, each of the clusters 107 iscomprised of a 2×2 hierarchy of four cells, called a logical cluster.FIGS. 2A and 2B show examples of individual cells 200 and 250. Cell 200performs multiple logic functions on two input signals (A and B) andprovides an output signal X. In the currently preferred embodiment, cell200 is comprised of an XOR gate 201, a two-input NAND gate 202, and atwo-input NOR gate 203. It should be noted, however, that in otherembodiments, cell 200 can include various other types and/orcombinations of gates. Cell 250 is comprised of cell 200 coupled with aD flip flop cell 260. The output X of cell 200 can be programmed toconnect directly to the data input D of the D flip flop gate 204 byactivating switch 218. The data input D can be accessed as a third inputof the combined cell 250. Each of the two input signals A and B and theD input of D flip-flop can be inverted or non-inverted, depending on thestates of switches 206-211. Activating switches 206, 208 and 210 causessignals A, B and D to be driven by drivers 212-214 to gates 201-204 in anon-inverted fashion. Activating switches 207, 209, and 211 causes theinput signals A, B and D to be inverted by inverters 215-217 beforebeing passed to gates 201-204. The six switches 212-217 can individuallybe turned on and off as programmed by the user.

Note that the XOR gate 201, NAND gate 202, and NOR gate 203 can also beused to perform XNOR, AND and OR by propagating the output signal to thenext stage, whereby the signal can be inverted as discussed above.

Three switches 219-221 are respectively coupled to the outputs of thethree gates 201-203. Again, these switches are programmable by the user.Thereby, the user can specify which of the outputs from the gates201-203 is to be sent to driver 224 as the output X from cell 200.

The aforementioned switches 206-211, 218-221 are comprised ofbi-directional, program-controlled passgates. Depending on the state ofthe control signal, the switches are either conducting (i.e. passes asignal on the line) or non-conducting (i.e. does not pass the signal onthe line). Switches mentioned in the following sections are similarlycomprised of program-controlled pas sgates.

Referring now to FIG. 3A, a logical cluster 107 is shown. In thecurrently preferred embodiment, logical cluster 107 is comprised of fourcells 301-304 and a D flip-flop 305, twenty five switches 306-330, andfive intraconnection lines 331-335. D flip flop 305 and cell 304 form acell 361, such as cell 250 described with respect to FIG. 2 a. TheIntraconnection lines 331-335 and switches 306-330 form the I-Matrix.I-Matrix provide connectability of the output, X, of each of the fourcells 301-304, and the output X of the D flip-flop 305 to at least oneinput of each of the other three cells and the D flip-flop. For example,the output X of cell 301 can be connected to input A of cell 302 byenabling switches 306 and 307. Likewise, the output X of cell 301 can beconnected to input B of cell 303 by enabling switches 306 and 310.Output X of cell 301 can be connected to input A of cell 304 by enablingswitches 306 and 308. Output X of cell 301 can be connected to input Dof the D flip-flop cell 305 by enabling switches 306 and 309.

Similarly, the output X from cell 302 can be connected to input A ofcell 301 by enabling switches 311 and 312. The output X from cell 302can be connected to input A of cell 303 by enabling switches 311 and315. The output X from cell 302 can be connected to input B of cell 304by enabling switches 311 and 313. Output X of cell 302 can be connectedto input D of the D flip-flop cell 305 by enabling switches 311 and 314.

Similarly, the output X from cell 303 can be connected to input B ofcell 301 by enabling switches 326 and 327. The output X from cell 303can be connected to input A of cell 302 by enabling switches 326 and328. The output X from cell 303 can be connected to input B of cell 304by enabling switches 326 and 329. Output X of cell 303 can be connectedto input D of the D flip-flop cell 305 by enabling switches 326 and 330.

For cell 304, the output X from cell 304 can be connected to input B ofcell 301 by enabling switches 316 and 317. The output X from cell 304can be connected to input B of cell 302 by enabling switches 316 and318. The output X from cell 304 can be connected to input A of cell 303by enabling switches 316 and 319. Output X of cell 304 can beprogrammably connected to input D of the D flip-flop cell 305 byenabling switch 218 in FIG. 2A.

With respect to cell 305, its output is connectable to the A input ofcell 301 by enabling switches 320 and 321; the B input of cell 302 byenabling switches 320 and 322; the B input of cell 303 by enablingswitches 320 and 325; the A input of cell 304 by enabling switches 320and 323; and the D input of cell 305 itself by enabling switches 320 and324.

It can be seen that each output of the cells 301-304 and of the Dflip-flop 305 is connectable to the input of each of its neighboringcells and/or flip-flop inside the cluster.

In the currently preferred embodiment of the present invention, eachlogical cluster is connectable to all the other logical clusters insideeach logical block through passgate switches extending the I-Matrix fromneighboring clusters inside each logical block. FIG. 3B illustrates theextension of I-Matrix intraconnection lines 331-335 of the cells 301-304and the D flip-flop 305 of a logical cluster 107 to a neighboringlogical cluster 107 through the passgate switches 336-355 within thesame logical block.

In the currently preferred embodiment of the present invention, eachlogical block is connectable to all the other logical blocks of theFPGA. This is accomplished by implementing an architecture with multiplelayers of interconnections. It is important to note that this multiplelayers routing architecture is a conceptual hierarchy, not a process ortechnology hierarchy and is hence readily implementable with today'ssilicon process technology. The bottom most layer of interconnections isreferred to as the “block connectors”. A set of block connectorsprovides the access and interconnections of signals within an associatedlogical block (which is consisted of four logical clusters or 16 cells).Thereby, different sets of logical clusters within the same logicalblock are connectable to any of the other logical clusters within thatgroup through the use of extended I-Matrix and/or block connectors.Again, programmable bi-directional passgates are used as switches toprovide routing flexibility to the user.

The next level of connections is referred to as the “level 1 MultipleLevel Architecture (MLA)” routing network. The level 1 MLA routingnetwork provides the interconnections between several sets of blockconnectors. Programmable passgates switches are used to provide userswith the capability of selecting which of the block connectors are to beconnected. Consequently, a first logical block from one set of logicalblock groups is connectable to a second logical block belonging to thesame group. The appropriate switches are enabled to connect the blockconnectors of the first logical block to the routing lines of the level1 MLA routing network. The appropriate switches of the level 1 MLArouting network are enabled to provide the connections to the blockconnectors of the second logical block to the routing lines of the level1 MLA routing network. The appropriate switches are enabled to connectthe routing lines of the level 1 MLA routing network that connected tothe block connectors of the first and the second logical blocks.Furthermore, the user has the additional flexibility of programming thevarious switches within any given logical block to effect the desiredintraconnections between each of the cells of any logical block.

The next level of connections is referred to as the “level 2 MultipleLevel Architecture (MLA)” routing network. The level 2 MLA provides theinterconnections to the various level 1 MLA to effect access andconnections of a block cluster. Again, bi-directional passgate switchesare programmed by the user to effect the desired connections. Byimplementing level 2 MLA routing network, programmable interconnectionsbetween even larger numbers of logical blocks is achieved.

Additional levels of MLA routing networks can be implemented to provideprogrammable interconnections for ever increasing numbers and groups oflogical blocks, block clusters, block sectors, etc. Basically, thepresent invention takes a three dimensional approach for implementingrouting. Signals are routed amongst the intraconnections of a logicalblock. These signals can then be accessed through block connectors androuted according to the programmed connections of the block connectors.If needed, signals are “elevated” to the level 1 MLA, routed through thelevel 1 MLA routing network, “de-elevated” to the appropriate blockconnectors, and then passed to the destination logical block.

If level 2 MLA routing network is required, some of the signals areelevated a second time from a level 1 MLA routing network line to thelevel 2 MLA routing network, routed to a different set of level 2 MLArouting network line, and “de-elevated” from the level 2 MLA routingnetwork line to a Level 1 MLA routing network line. Thereupon, thesignals are “de-elevated” a second time to pass the signal from thelevel 1 MLA to the appropriate block connectors of the destinationlogical block. This same approach is performed for level 3, 4, 5, etc.MLAs on an as needed basis, depending on the size and density of theFPGA. Partial level n MLA can be implemented using the above discussedmethod to implement a FPGA with a given cell array count.

FIG. 4A shows an example of a logical cluster and the associatedvertical block connectors within the logical block. In the currentlypreferred embodiment, each cell in a logical cluster is accessible fromthe input by two vertical block connectors and each output of the cellin a logical cluster is accessible to two of the vertical blockconnectors. For example, input A of cell 301 is accessible to thevertical block connectors 451 (BC-V11) and 453 (BC-V21) through switches467, 462 respectively, input B of cell 301 is accessible to the verticalblock connectors 452 (BC-V12) and 454 (BC-V22) through switches 466, 468respectively, output X of cell 301 is accessible to the vertical blockconnectors 455 (BC-V31) and 458 (BC-V42) through switches 460, 459respectively. Input A of cell 302 is accessible to the vertical blockconnectors 453 (BC-V21) and 455 (BC-V31) through switches 463, 464respectively, input B of cell 302 is accessible to the vertical blockconnectors 454 (BC-V22) and 456 (BC-V32) through switches 469, 470respectively, output X of cell 302 is accessible to the vertical blockconnectors 452 (BC-V12) and 457 (BC-V41) through switches 461, 465respectively. Input A of cell 303 is accessible to the vertical blockconnectors 451 (BC-V11) and 453 (BC-V21) through switches 485, 476respectively, input B of cell 303 is accessible to the vertical blockconnectors 452 (BC-V12) and 454 (BC-V22) through switches 480, 476respectively, output X of cell 303 is accessible to the vertical blockconnectors 455 (BC-V31) and 458 (BC-V42) through switches 472, 471respectively. The input A of cell 304 is accessible to the verticalblock connectors 453 (BC-V21) and 455 (BC-V31) through switches 477, 478respectively, input B of cell 304 is accessible to the vertical blockconnectors 454 (BC-V22) and 456 (BC-V32) through switches 482, 484respectively, output X of cell 304 is accessible to the vertical blockconnectors 452 (BC-V12) and 457 (BC-V41) through switches 475, 474respectively. D flip-flop cell 305 input is accessible to the verticalblock connectors 454 (BC-V22) and 455 (BC-V31) through switches 473, 479respectively, output X of cell 305 is accessible to the vertical blockconnectors 452 (BC-V12) and 457 (BC-V41) through switches 483, 486respectively.

In similar fashion, FIG. 4B shows the possible connections correspondingto horizontal block connectors and the logical cluster shown in FIG. 4A.Input A of cell 301 is accessible to the horizontal block connectors 402(BC-H12) and 404 (BC-H22) through switches 409, 413 respectively, inputB of cell 301 is accessible to the horizontal block connectors 401(BC-H11) and 403 (BC-H21) through switches 415, 416 respectively, outputX of cell 301 is accessible to the horizontal block connectors 405(BC-H31) and 408 (BC-H42) through switches 421, 428 respectively. InputA of cell 302 is accessible to the horizontal block connectors 402(BC-H12) and 404 (BC-H22) through switches 411, 414 respectively, inputB of cell 302 is accessible to the horizontal block connectors 401(BC-H11) and 403 (BC-H21) through switches 433, 417 respectively, outputX of cell 302 is accessible to the horizontal block connectors 405(BC-H31) and 408 (BC-H42) through switches 418, 424 respectively. InputA of cell 303 is accessible to the horizontal block connectors 404(BC-H22) and 406 (BC-H32) through switches 419, 426 respectively, inputB of cell 303 is accessible to the horizontal block connectors 403(BC-H21) and 405 (BC-H31) through switches 420, 425 respectively, outputX of cell 303 is accessible to the horizontal block connectors 402(BC-H12) and 407 (BC-H41) through switches 410, 427 respectively. Theinput A of cell 304 is accessible to the horizontal block connectors 404(BC-H22) and 406 (BC-H32) through switches 422, 430 respectively, inputB of cell 304 is accessible to the horizontal block connectors 403(BC-H21) and 405 (BC-H31) through switches 423, 429 respectively, outputX of cell 304 is accessible to the horizontal block connectors 402(BC-H12) and 407 (BC-H41) through switches 412, 434 respectively. Dflip-flop cell 305 input is accessible to the horizontal blockconnectors 403 (BC-H21) and 406 (BC-H32) through switches 436, 431respectively, output X of cell 305 is accessible to the horizontal blockconnectors 401 (BC-H11) and 408 (BC-H42) through switches 432, 435respectively.

FIGS. 4A and 4B illustrate the vertical and horizontal block connectorsaccessing method to the upper left (NW) logical cluster inside a logicalblock in the currently preferred embodiment. The lower left (SW) clusterhas the identical accessing method to the vertical block connectors asthose of the NW cluster. The upper right (NE) cluster has similaraccessing method to those of the NW cluster with respect to the verticalblock connectors except the sequence of vertical block connector accessis shifted. The vertical block connectors 451-458 can be viewed aschained together as a cylinder (451, 452, . . . , 458). Any shift, sayby 4, forms a new sequence: (455, 456, 457, 458, 451, 452, 453, 454).Instead of starting with vertical block connectors 451 and 453 accessingby cell 301 in the NW cluster as illustrated in FIGS. 4A, the cell 301in the NE cluster is accessible to VBCs 455 and 457. The numbering is“shifted” by four. The access labeling of the lower right (SE) clusterto the VBCs is identical to those of NE cluster.

Similarly, the horizontal block connectors access to the NW cluster isidentical to those of the NE cluster and the SW cluster is identical tothe SE cluster while the horizontal block connectors access to the SWcluster is shifted by four compared with those of NW cluster.

In the currently preferred embodiment, sixteen block connectors are usedper logical block (i.e. four clusters, or a 4×4 cell array). Adding alevel 1 MLA routing network allows for the connectability for a blockcluster (an 8×8 cell array). Adding level 2 MLA routing networkincreases the connectability to a block sector (16×16 cell array).Additional levels of MLA routing network increases the number of blocksectors by factors of four while the length (or reach) of each line inthe MLA routing network increases by factors of two. The number ofrouting lines in the level 2 MLA is increased by a factor of two; sincethe number of block sectors increased by a factor of four, on a per unitarea basis, the number of routing lines in the next level of hierarchyactually decreases by a factor of two.

FIG. 5A shows a logical block with associated sixteen block connectorsand level 1 MLA routing lines associated with the logical block. Thesixteen block connectors 501-516 are depicted by heavy lines whereas thesixteen level 1 MLA routing network lines 517-532 are depicted bylighter lines. Note that the length or span of the block connectorsterminates within the logical block while the length of the level 1 MLArouting network lines extends to neighboring logical blocks (twice thelength of the block connectors).

Both block connectors and level 1 MLA routing network lines aresubdivided into horizontal and vertical groups: vertical blockconnectors 501-508, horizontal block connectors 509-516, vertical level1 MLA routing network lines 517-524, and horizontal level 1 MLA routingnetwork lines 525-532.

In the currently preferred embodiment, there are twenty four level 1 MLAturn points for the sixteen level 1 MLA routing network lines within thelogical block. In FIG. 5A, the twenty four turn points are depicted asclear dots 541-564. A MLA turn point is a programmable bi-directionalpassgate for providing connectability between a horizontal MLA routingnetwork line and a vertical MLA routing network line. For example,enabling level 1 MLA turn point 541 causes the horizontal level 1 MLArouting network line 526 and vertical level 1 MLA routing network line520 to become connected together. FIG. 5B shows level 1 MLA turn point541. Switch 583 controls whether level 1 MLA routing network line 526 isto be connected to level 1 MLA routing network line 520. If switch isenabled, then level 1 MLA routing network line 526 is connected to level1 MLA routing network line 520. Otherwise, line 526 is not connected toline 520. Switch 583 is programmable by the user. The turn points areplaced as pair-wise groups with the objective of providing switchingaccess connecting two or more block connectors first through the blockconnector to level 1 MLA exchange networks and then connecting selectedlevel 1 MLA routing lines by enabling the switches. The level 1 MLAlines are used to connect those block connectors that reside in separatelogical blocks within the same block cluster.

Referring back to FIG. 5A, there are eight block connector to level 1MLA exchange networks 533-540 for each logical block. These exchangenetworks operate to connect certain block connectors to level 1 MLAlines as programmed by the user. FIG. 5C shows the exchange network 537in greater detail. The block connector to level 1 MLA routing exchangenetwork has eight drivers 575-582. These eight drivers 575-582 are usedto provide bi-directional drive for the block connectors 501, 502 andlevel 1 MLA lines 517, 518. For example, enabling switch 565 causes thesignal on block connector 501 to be driven by driver 575 onto the level1 MLA line 517. Enabling switch 566 causes the signal on level 1 MLAline 517 to be driven by driver 576 onto the block connector 501.Enabling switch 567 causes the signal on block connector 501 to bedriven by driver 577 onto the level 1 MLA line 518. Enabling switch 568causes the signal on level 1 MLA line 518 to be driven by driver 578onto the block connector 501.

Similarly, enabling switch 569 causes the signal on block connector 502to be driven by driver 579 onto the level 1 MLA line 517. Enablingswitch 570 causes the signal on level 1 MLA line 517 to be driven bydriver 580 onto the block connector 502. Enabling switch 571 causes thesignal on block connector 502 to be driven by driver 581 onto the level1 MLA line 518. Enabling switch 572 causes the signal on level 1 MLAline 518 to be driven by driver 582 onto the block connector 502. Switch573 is used to control whether a signal should pass form one blockconnector 501 to the adjacent block connector 584 belonging to theadjacent logical block.

Likewise, switch 574 is used to control whether a signal should passform one block connector 502 to the adjacent block connector 585belonging to the adjacent logical block.

FIG. 6 shows the routing network for a block cluster. The block clusteris basically comprised of four logical blocks which can beinterconnected by the level 1 MLA exchange networks 533-540. It can beseen that there are thirty-two level 1 MLA routing network lines.

FIG. 7A shows the block diagram for a block sector. The block sector iscomprised of four block clusters 701-704. As discussed above, the blockclusters are interconnected by block connectors and level 1 MLA routingnetwork lines. In addition, the block sector is also comprised ofsixty-four level 2 MLA routing network lines and sixty-four level 2 tolevel 1 exchange networks to provide connectability between level 1 MLArouting network and level 2 MLA routing network. The level 1 to level 2MLA routing exchange networks are depicted by rectangles in FIG. 7A.Furthermore, there are forty-eight level 2 MLA turn points associatedwith each of the four logical blocks within the block sector.Consequently, there are one hundred and ninety-two level 2 MLA turnpoints for the block sector.

FIG. 7B shows a sample level 1 to level 2 MLA routing exchange network705. It can be seen that switch 710 is used to control whether a signalshould pass between level 1 MLA line 709 and level 2 MLA line 708.Switch 711 is used to control whether a signal should pass between level1 MLA line 709 and level 2 MLA line 707. Switch 712 is used to controlwhether a signal should pass between level 1 MLA line 706 and level 2MLA line 708. Switch 713 is used to control whether a signal should passbetween level 1 MLA line 706 and level 2 MLA line 707. Switch 714 isused to control whether a signal should pass form one level 1 MLA line709 to the adjacent level 1 MLA line 716 belonging to the adjacent blockcluster. Likewise, switch 715 is used to control whether a signal shouldpass form one level 1 MLA line 706 to the adjacent level 1 MLA line 715belonging to the adjacent block cluster.

FIG. 8A shows a sector cluster. The sector cluster is comprised of fourblock sectors 801-804 with their associated block connectors, level 1,and level 2 MLA routing network lines and exchange networks. Inaddition, there are one hundred and twenty-eight level 3 MLA routingnetwork lines, providing connectability between the level 2 MLA linesthat belong to different block sectors 801-804 within the same sectorcluster 800. There are ninety-six level 3 MLA turn points associatedwith the level 3 MLA lines for each of the block sector 801-804 (i.e.three hundred and eighty-four total level 3 MLA turn points for thesector cluster). Furthermore, there are thirty-two level 2 to level 3MLA routing exchange networks associated with each of the four blocksector 801-804. Hence, there are total of one hundred and twenty-eightlevel 3 MLA routing exchange network for providing programmableconnectability between the various level 2 and level 3 MLA lines.

FIG. 8B shows an example of a level 2 to level 3 MLA routing exchangenetwork 805. It can be seen that enabling switch 810 causes a signal onthe level 2 MLA line 808 to be connected to the level 3 MLA line 806.Disabling switch 810 disconnects the level 2 MLA line 808 from the level3 MLA line 806. Enabling switch 811 causes a signal on the level 2 MLAline 808 to be connected to the level 3 MLA line 807. Disabling switch811 disconnects the level 2 MLA line 808 from the level 3 MLA line 807Likewise, enabling switch 812 causes a signal on the level 2 MLA line809 to be connected to the level 3 MLA line 806. Disabling switch 812disconnects the level 2 MLA line 809 from the level 3 MLA line 806.Enabling switch 813 causes a signal on the level 2 MLA line 809 to beconnected to the level 3 MLA line 807. Disabling switch 813 disconnectsthe level 2 MLA line 809 from the level 3 MLA line 807.

In the present invention, larger and more powerful FPGAs can be achievedby adding additional logic sector clusters which are connected byadditional levels of MLA routing networks with the corresponding MLAturn points and exchange networks.

In one embodiment of the present invention, each of the five I-Matrixlines (331-335, FIG. 3A) can be extended to provide connectabilitybetween two adjacent I-Matrix lines belonging to two different clusters.The passgate switches 336-340, 341-345, 346-350, and 351-355 in FIG. 3Bare examples of four different sets of I-Matrix line extension switches.This provides further flexibility by providing the capability of routinga signal between two adjacent clusters without having to be routedthrough the use of block connectors.

Similarly, block connectors can be extended to provide connectabilitybetween two adjacent block connectors belonging to two different logicalblocks. Switch 573 of FIG. 5C illustrates such block connector extensionconnecting block connector 501 to block connector 584 through switch573. This provides further flexibility by providing the capability ofrouting a signal between two adjacent logical blocks without having tobe routed through the level 1 MLA lines and associated MLA exchangenetworks. This concept can be similarly applied to the level 1 MLA linesas well. Switch 714 of FIG. 7B shows an example where level 1 MLA line709 is extended to connect to level 1 MLA line 716 by enabling switch714. This provides further flexibility by providing the capability ofrouting a signal between two adjacent block clusters without having tobe routed through the level 2 MLA lines and associated MLA exchangenetworks.

Thus, an architecture with an intraconnect and interconnect scheme forprogrammable logic circuits is disclosed.

What is claimed is:
 1. A field programmable gate array architecture,comprising: (a) a first logical cluster having a first span in a firstdimension and having a second span in a second dimension, the clustercomprising a plurality of cells, each cell comprising: an output, atleast one input, and an input multiplexer coupled to each input; (b) afirst plurality of intraconnect conductors within the first and secondspans, wherein the output of each cell in the first logical cluster isselectively coupleable to at least one input multiplexer coupled to eachof the other cells in the first logical cluster by traversing a singleone of the first plurality of intraconnect conductors; (c) a secondlogical cluster having a third span in the first dimension and having aspan in the second dimension equal to the second span, the clustercomprising a plurality of cells, each cell having: an output, at leastone input, and an input multiplexer coupled to each input; (d) a secondplurality of intraconnect conductors within the second and third spans,wherein the output of each cell in the second logical cluster isselectively coupleable to at least one input multiplexer coupled to eachof the other cells in the second logical cluster by traversing a singleone of the second plurality of intraconnect conductors; (e) a thirdlogical cluster having a fourth span in the first dimension and a spanin the second dimension equal to the second span, the cluster comprisinga plurality of cells, each cell having: an output, at least one input,and an input multiplexer coupled to each input; (f) a third plurality ofintraconnect conductors within the second and fourth spans, wherein theoutput of each cell in the third logical cluster is selectivelycoupleable to at least one input multiplexer coupled to each of theother cells in the third logical cluster by traversing a single one ofthe third plurality of intraconnect conductors; (g) a fourth logicalcluster having a fifth span in the first dimension and a span in thesecond dimension equal to the second span, the cluster comprising aplurality of cells, each cell having: an output, at least one input, andan input multiplexer coupled to each input; (h) a fourth plurality ofintraconnect conductors within the second and fifth spans, wherein theoutput of each cell in the fourth logical cluster is selectivelycoupleable to at least one input multiplexer of each of the other cellsin the fourth logical cluster by traversing a single one of the fourthplurality of intraconnect conductors.
 2. The field programmable gatearray architecture of claim 1, further comprising: (i) a fifth pluralityof routing conductors having a sixth span in the first dimension and aspan in the second dimension equal to the second span, wherein theoutput of each cell in the first logical cluster is selectivelycoupleable to a plurality of input multiplexers in the second logicalcluster; and (j) a sixth plurality of routing conductors having aseventh span in the first dimension and a span in the second dimensionequal to the second span, wherein the output of each cell in the thirdlogical cluster is selectively coupleable to a plurality of inputmultiplexers in the fourth logical cluster, wherein at least one of therouting conductors in the fifth plurality of conductors is selectivelycoupleable to at least one of the routing conductors in the sixthplurality of conductors.
 3. A programmable logic circuit, comprising: aninput configured to receive a signal into the programmable logiccircuit; a plurality of cells coupled to the input, each of theplurality of cells configured to process the signal; a first set ofrouting lines configured to directly couple, through a first set ofprogrammable switches, to the plurality of cells to form logical blocksof cells, wherein input and outputs of cells of logical blocks areprogrammably coupled to the first set of routing lines; and a second setof routing lines, configured to couple directly and bidirectionally tothe first set of routing lines through a second set of programmableswitches, each routing line of the first set of routing linesselectively configured to be a source to drive a routing line of thesecond set of routing lines through the second set of programmableswitches and a sink to receive the signal through the second set ofprogrammable switches from the routing line of the second set of routinglines, wherein a span of the second set of routing lines is longer thana span of the first set of routing lines.
 4. The programmable logiccircuit of claim 3, wherein the second set of programmable switchescomprises components selected from the group consisting of switches,programmable pas sgates and program controlled drivers/receivers.
 5. Anintegrated circuit, comprising: a first region comprising: a firstplurality of cells located along a first dimension and a seconddimension, wherein the first region has a first span along the firstdimension and a second span along the second dimension; a plurality ofswitches; and a first plurality of conductors located within the firstregion, wherein each conductor of the first plurality of conductors toselectively couple to inputs and outputs of cells of the first pluralityof cells and conductors of the first plurality of conductors through theplurality of switches and wherein the first plurality of conductors spancells of the first plurality of cells along the first dimension and thesecond dimension, wherein the first plurality of conductors comprises: afirst conductor having a first span along the first dimension; a secondconductor having a second span along the first dimension; a thirdconductor having a third span along the second dimension; and a fourthconductor having a fourth span along the second dimension; wherein thefirst span of the first region is greater than the first span of thefirst conductor and the first span of the first conductor is greaterthan the second span of the second conductor, wherein the second span ofthe first region is greater than the third span of the third conductorand the third span of the third conductor is greater than the fourthspan of the fourth conductor.
 6. The integrated circuit of claim 5,further comprising a second region, located within the first region,having a span along the first dimension, comprising: a subgroup of cellsof the first plurality of cells located in the second region, whereinthe span of the second region is less than the second span of the secondconductor; a fifth conductor of the first plurality of conductorslocated within the second region having a fifth span equal to the spanof the second region along the first dimension.